My '87 will occasionaly crank but not start---it has happened to me about 3 or 4 times since I bought it last November and the PO (i.e. Dad) has had similar problems for a while. We have always assumed this was a VATs problem since it will resolve itself after the usuall 4 minute delay.

I piped up about this over in Calderone's thread
http://forums.corvetteforum.com/c4-t...s-trouble.html
only to learn that I was mis-informed and that VATs should be disabling the cranking as well.

I checked for codes this morning (crank but no start with code 46 can be a valid VATs issue) and found none. This suggests an entirely different problem, but...I have one question:

Will an intermittent VATs problem store a code 46 permanently (i.e. until cleared) or will the code be cleared when/if the VATs issue resolves itself?

My assumption has always been that my problem is due to the key not being positioned quite right causing a misread of the resistor pellet. If the code 46 is cleared when the key is repositioned and car started then the intermittent problem may indeed be VATs. If the code is permanently stored then the symptom table clearly indicates this is not a VATs problem.

Either way, I can't do much about it while it remains intermittent and I have engine swap plans that will resolve the problem if they come to fruition.

 

my understanding from the 91 fsm was that the codes had to be cleared -did not mention that VATS was exempt- and I doubt that it would be.

VATS disables crank by disabling starter relay -which is the first clue we get- and the CCM also will not send a fuel enable -meaning injectors pulse- signal to ecm. far as I can tell, does not disable FP, only injectors pulse, but may be wrong.

this is 91, and some yrs did not have the CCM, but have the vats module.

vats gives "no crank no click" mode, 8a-30-4 in my book, and you have "cranks but no run"

as you know, the fault tree is pages. if you don't have fsm or Chilton's, you can describe the symptoms and someone or some dozens will chime in.

jc

 

Thank you for your reply.

I do have the FSM. In the Electrical Dagnosis supplement VATS System Diagnosis section (page 8A-133-10) there is a symptom table with four entries:

1. No Crank, ECM Code 46 present
2. Crank but no Start, ECM Code 46 Present
3. No Crank, No ECM Code 46
4. Crank but no Start, No ECM Code 46

Quoting the manual:

"The first of these is almost certain to be a VATS problem. The second and third can be caused by VATS but may also be caused by other systems on the vehicle. The fourth symptom is definitely not related to VATS."

I have the 4th symptom intermittently. If the code isn't reset by a successful start then I'll have to dive into section 6E to figure it out if/when it becomes a hard fault. Thus my question, do some codes reset or do they all stick 'til cleared?

 

I think I read that they all remain in history, for the reasons you can see, clues to help troubleshoot. You don't have CCM? I read that in CCM pages if I recall.

would #4 always show a code? unless it was related to a sensor, it might not.

joe

 

Sorry, I'm not sure what CCM is. Owners manual? I do have that & will take a look.

As for your second question, no #4 can be many things, not all of which set codes---section 6E covers a lot of ground.

I guess I'm indulging in a bit of wishful thinking hoping it's just a reset VATS problem.

 

CCM is central control module. sends many signals to ECM. I know- learning the corvette lingo is difficult, TPS, ICM, IAT, ICV, etc. even PASS key is not self explanatory -pers access sec sys.

on ccm autos, ccm sends the signals from pass to ecm, to enable start relay and "enable fuel." mostly it monitors driver info stuff, oil info, etc.

if you don't have you have the vats module. a lot of important differences betwen years.

joe

 

..... Per your own admission , you have symptom #4 and you quote the manual "The fourth symptom is definitely not related to VATS " yet you still pursue a VATS fault ????

..... What troubleshooting have you done related to the cranks - no start issue ? Is this condition evident only when engine is cold ? warm ? Are you getting any spark at all ? Fuel pressure ? Whats the battery voltage during crank ? Check the engine coolant temp sensor ? Flutter the throttle while cranking ? Don't dwell on VATS when all indications are that its not at fault ................

 

I almost totally agree, c409, except that he is noticing that 2 and 4 are the same, except for the 46. so he wonders if the code was not set, and he chases "all other" solutions when it is vats.

may be overthinking it. not too uncommon. the reaction of the rational mind when facing the computer.

joe

 

like posted VATS disables the starter. Most of the early cars had the key switch replaced, the new one fixed most VATS problems.
Try some old school troubleshooting next time it won't start. Pull a plug wire and see if it sparks or will shock someone. Or get a can of starting fluid and spray a shot at the throttlebody.
Listen for the fuel pump to run, you might have an old relay with dirty contacts.

JS

 

You have a FUEL prroblem...not a VATS issue. I am still uncertain as to why everytime there is a run/start problem everyone gets their finger cocked and takes a shot at the VATS.

If you have Bosch III inj they are harder to start than the stock mule-tics.
If you have stock mule-tic then you probably need Bosch-III injectors.
Check the fuel pressure.
Fuel filter.
Fuel pump & screen.
Eng coolant temp sensor ( has everything to do with warm restarts)
Fuel pump RELAY...bad relay means longer cranking time before the engine can fire.
An engine that cranks but does not fire most often has a problem with a reference signal to/from somewhere or simple fuel flow. Because the entire electrical system is operated by completing ground pathways to inj, IAC motors, etc, the plugs and connections are CRITICAL for normal operation.Let them get dirty and you WILL have problems.

UNLESS your security system has been "bubba'd" here is the way it works..

The VATS is an anti theft system, not an alarm as most folks call it. It works by interrupting necessary function of the engines control system. Fuel injection, and starter. No starter, no start. Get it to crank, you still need fuel. No legit starter pathway, no fuel inj authorization. Its a pretty foolproof anti theft system. Tripping it by the illegit opening of a door without a key in the lockswitch, trips it and sounds the alarm. NOT making contact with the Ign key pellet in the ign switch as that switch is rotated triggers VATS. The key pellet is only a measured resistor. That circuit MUST be complete as the ign turns to RUN or the system will not get the authorization to enable starter and fuel injectors. The key switch is simple. 2 tabs inside that touch the key pellet. Not a big deal They have to be caked on crap to prevent contact OR be so worn or bent that the pellet does not touch.
Insert the key and slide it in/out one time THEN rotate. This usually solves the bad key switch issue. Replacement is the fix. Switches wear.
VATS sets for a min 4 min up to 15 min interrupt. ANY attempt to start prior to the VATS reset will again place the system in a random interrupt mode again. This can go on ALL DAMN DAY if you are impatient and try to turn that key 3 seconds too soon.......
When is too soon? possibly ANYTIME under 20 minutes.
The theory is that the car thiefs worst case scenario is a car that he can;t steal in 60 seconds or less. MANY are gone in 20 seconds. If VATS locks out the crutial systems for 15 minutes, the word gets around and the thieves move on....I have not heard of a Corvette being hot wired and stolen since 1989 or about . I have heard of many attempts by amature thieves that tore things up a bit, but they failed to take the car.

IF you had a VALID VATS interrupt, you would see the "security" light blinking when the ign key was turned and nothing happened. That light cycles with the others whenever the key is turned past on to start position. If it were VATS related, it would continue to flash.

 

fuel pump relay,fuel enable relay

 

Thank you all for your comments.

I thought it was VATS because I was told it was VATS, and it behaved like VATS (as it was described to me), and never questioned that assumption til I revealed my ignorance in Calderone's thread. When I finally read the manual myself it became clear it probably isn't VATS but wanted to double check that one point about the code resetting to be sure. Even there it turns out I was "over thinking" things and, by skipping to the diagnostic charts, had missed the clear statement in the Clearing Trouble Codes section at the beginning of section 6E:

"When the ECM sets a trouble code the "SERVICE ENGINE SOON" light will com "ON" and a trouble code will be stored in memory. If the problem is intermittent, the light will go out after 10 seconds, when the fault goes away. However, the trouble code will stay in the ECM memory until the battery voltage to the ECM is removed."

That answers my question. Clearly my issue is not VATS & I will have to diagnose it further as it occurs. Some kind of fuel or injector issue seems most likely---the PO's mechanic was thinking along those lines & replaced the fuel pump before I bought it. (He didn't charge for it though, because the problem only seemed to occur when using a specific, very old and worn, ignition key. Thus began the VATS misinterpretation.)

So, again, my question is answered. If it occurs again within the 45 day thread time limit I'll post any further questions here.

 

dude, I believed I understood your question all along. I guarantee you many people learned something from the post.

"history" means forever -or until the negative of the battery is removed.

joe

 

Which is why I probably shouldn't be so active on the internet.

 

The historical error codes are erased if there are 50 successive starts without any errors.

You might be able to get the 50 restarts just by turning the ignition on and off 50 times. I was working on the code for my '86 (BUA) when I took a break and came here, so it's open in the background and I just checked it. It does the reset on the 51st restart. It's not clear (without a lot of poking around in the code) if the engine actually has to run to do the reset.

It's probably a lot easier to pop the ECM connector next to the positive battery terminal... :-)

 

Interesting...

I think there have been less than 10 restarts between the last time it acted up (Tuesday night) and I checked for codes (Saturday morning), so don't think any code was set.

Thank you for your reply.

I'm going to have to think about what to carry with me to evaluate this when it happens again.

 

just reaD SOME 7-8 gm TECH SERVICE BULLETINS for c4's. one was for 86-87, with intermittent no start, may or may not set a code. the fix was a diff ign key lock with tighter clearances, also a longer pass key.

the bull # wAS 87-140. I saved it to e mail and can send it if you pm. if you want it and can't locate it. I figure the bulletins are on this site but got this from corvettecentral site.

joe

 

Interesting...that jives nicely with the "bad key" theory.

I'll PM my email address to you in a minute.

Thanks,

Wayne

 

Got it, thanks.

It's interesting the service bulletin doesn't mention whether a code is set. I still have the key that causes (I thought) the problem. I think I'll try reproducing the problem using that key with my scanner hooked up & see what I learn. I probably won't get to it till next weekend but will post the results when I do.

Wayne

 

That service was the repair and fix GM had for the VATs problems eairly on. Again it does not sound like you have a VATS problem. Gm found out that the lock cyl had enough play in it that at times the key did not get a good read. So the fix was to replace the lock cyc along with a longer key.. In over 30 years I have never seen a Vats mess up and still crank.....